The present invention relates to pickup arms for capacitance disk records, and particularly to a signal pickup device which includes a jitter compensation and tracking control system for a capacitance detection type stylus which rests over several tracks of a grooveless capacitance disk.
A signal pickup device for grooveless capacitance disk records, as shown and described in U.S. Pat. No. 4,160,268 assigned to the same assignee of the present invention, comprises a jitter compensation and tracking control unit for counteracting the jitter movement of the capacitance detection stylus and for keeping it on the right track of the record that spins at a considerably high speed. The stylus is secured to the free end of a cantilever or stylus supporting arm, the other end of which is pivotally coupled with the jitter compensation and tracking control unit. Since the jitter compensation involves moving the stylus in a direction parallel to the track and to the record surface while the tracking control involves moving it in lateral directions, the cantilever should be coupled to the control unit by pivot bearings which are capable of such movements. Because of the high rotational speed of the record the stylus must be designed to exert a prescribed amount of pressure to the record and this pressure must be constant and small enough to avoid impairment of the record surface. Signal pickup devices which have hitherto been developed are not satisfactory in this respect. In the aforesaid prior art signal pickup device, the stylus control unit is mounted in a position tilted with respect to the bottom of the device housing and as a result the pivot bearings tend to exert a downward force component in addition to the horizontal components to the stylus in response to the signal applied to the control unit so that the record surface is damaged.